Projectors for tilt projection as referred to in Japanese Patent Publication No. JP-A-5-100311 are known. When described with reference to a projector for tilt projection installed on a desk or the like, the light source optical axis of a light source is substantially flush with the central axis of the image formation area of an electro-optic modulator and the projection optical axis of a projection system is shifted upward from the central axis of the image formation area of the electro-optic modulator.
Despite recent increasing demand to reduce the thickness of a projector, the portion of the upper surface of the projector housing in the projector for tilt projection corresponding to the area in which a projection system is disposed and projects from includes the portion of the projector housing corresponding to the area in which other optical systems (e.g., the light source and a superimposing lens) are also disposed. As such, the height of the upper surface of the housing is relatively high, and reducing the thickness of the projector is difficult.
The thickness of the projector may not be reduced by lowering the vertical position of the projection system disposed in the housing as compared to that in related art alone, because tilt projection to the projection surface may not be performed properly by changing the vertical position of the projection system without changing the vertical positions of the other optical systems.
Dimensional design and configuration problems are not limited only to projectors for tilt projection, but similar problems occur in projectors in which the projection optical axis of the projection system is substantially flush with the central axis of the image formation area of the electro-optic modulator. For example, in a projector including a large-diameter projection lens used as the projection system, the upper end of the projection system may be higher than the upper ends of other optical systems (the light source and the superimposing lens, for example) depending on the size of the lens diameter, even when the projection optical axis of the projection system is substantially flush with the central axis of the image formation area of the electro-optic modulator. In this case as well, the resulting portion of the upper surface of the projector housing that corresponds to the area in which the projection system is disposed and projects from includes the portion corresponding to the area in which other optical systems (the light source and the superimposing lens, for example) are disposed, so that the height of the upper surface of the housing is relatively high, and hence it is not easy to reduce the thickness of the projector.
Alternatively, the height of the upper surface of the housing may not be exclusively determined by the vertical position of the projection system disposed in the housing, but rather also by the size of the light source. For example, when a relatively large reflector is used in the light source, the portion of the upper surface of the housing that corresponds to the area in which the light source is disposed and projects from includes the portion corresponding to the area in which other optical systems (the superimposing lens and the projection system, for example) are disposed, so that the height of the upper surface of the housing is relatively high, and hence it is not easy to reduce the thickness of the projector. In this case, the thickness of the projector may be reduced by reducing the size of the reflector. Unfortunately, this approach also decreases the brightness obtained by the projector.